This means if you measure, "up" for the spin of one photon from an entangled pair, the spin of the other, measured an instant later, will be "down" - even if the two are on opposite sides of the world. The feat showed that the particles of light can retain a unusual type of interconnectedness, known as quantum entanglement, even when flung to opposite ends of a country, researchers from China report in the June 16 Science.
In quantum physics, entangled particles remain connected so that actions performed by one affects the behaviour of the other, even if they are separated by huge distances. Any attempt to eavesdrop would disturb the particles and be discovered. Encode that message using the pattern of entangled particle states on that end.
As useful as it might someday be, quantum effects are very sensitive to interference from the environment.
In 2003, Pan Jianwei, a professor of quantum physics at the University of Science and Technology of China, started work on a satellite-based system created to beam entangled photon pairs down to ground stations.
Photons are extremely fragile: they travel more smoothly in the near vacuum of space than in the earth's atmosphere.
"There are not many experiments which test links between gravity and quantum physics", he told Science. "So how can you do similar experiments at thousand-kilometers distance scale and with the optical elements vibrating and moving at a speed of 8 kilometers per second [5 miles per second]?"
Photo taken on November 26, 2016 shows a quantum communication ground station in Xinglong, north China's Hebei Province.
Once scoffed at by Einstein, quantum entanglement is a odd phenomenon that occurs when two or more particles link up and instantaneously affect each other, regardless of how far apart they are. This is the significance of the Chinese discovery, described in a paper in the journal Science. One possibility is that entangled photons could be important for telecommunications.
Previously, entanglement distribution had only been achieved at a distance up to 100-km due to photon loss in optical fibres or terrestrial free space. "We have done something that was absolutely impossible without the satellite".
The development of the satellite is part of the larger plan to developing a new kind of internet that is more secure that what is now used. One of these beams was used to transmit the entangled photons, while the other served to receive the photons.
That technological achievement is unbelievable, says physicist Harald Weinfurter of Ludwig-Maximilians-Universität in Munich.
"I'm personally convinced that the internet of the future will be based on these quantum principles". "China is now clearly taking the world leadership in this area of quantum communication", Jennewein says. The satellite will overfly Beijing, establish a quantum key with a ground station, then establish another key with another station when it overflies Austria. The obtained link efficiency is orders of magnitude higher than that of the direct bidirectional transmission of two photons through telecommunication fibers. This required focusing the photons through special receivers, with the ground stations using adaptive optics.
At its core, the technique is similar to encryption methods now used to protect information transmitted by Internet users, the British media outlet explained, but unlike that method, the new quantum-based technique hides the key required to unscramble the encrypted data in photons.